Ester-type synthetic lubricants



'tively, or lower.

Patented Feb. 9, 1954 UNITED srArss PATENT OFFICE ESTER-TYPE SYNTHETICLUBRICANTS Martin B. Neuworth, Brentwood, .Pa.,-a.ssignor to*Socony-Vacuum Oil Company, Incorporated, a corporation of New York .NoDrawing. Application October 7, 1949, Serial No. 120,225

:12 Claims. (Cl. 260485) This invention relates, broadl to -ester+typesynthetic lubricants, and. is .more particularly concerned. with theoily tetra-esters .cf adipic acid havinghigh viscosity indicesand lowpour points.

Tetra-estersof adipic acid arethepredomi .nant constituents of thereaction products obtained from the esterification ofaglycol orcofthiodiglycol with an adipic acid monoester. These tetra-esters have thegeneral structures:

.CO(OCHiGH c)nOOO ,QOOCHrCHzLS .(ICHzM H2); (CH2); R R000 000R 2 whereinR is a branched-chain aliphatic group and .n is an integer equal tooneor more.

The. tetra-esters of this invention are disinguishable from thepolyester resins disclosed inU. S. Patent No. 2,035,528. in the patent,the resinous products are produced'by reacting di carboxylic acids withmonohydric aicohols and with polyethyleneglycols in four different manners. Astudy of the working examples reveals that such reactions arecarried out using a molar proportion of monoester to glycol of 1:1,respec- In accordance with the present invention, however, it has beenfoundthat syn- .thetic. lubricants are produced onlywhen a true,

non-resinous ester is obtained. This necessitates a molar proportionof-'-monoester to-qglycol of. about 2 :1, respectively.

As is well known to those familiar with the art, a large variety orestershave been proposed for use as synthetic lubricants. However, whenthese products have been utilized they have been found to be wanting inone or more characteristics. Thus, when these products have had highviscosity indices and low pour points, the

viscosity has been poor. For example, it has been suggested to use thesimple neutral esters of a number of dicarboxylic acids, including:adipic acid. However, when the dicarboxylic acid has been esterifiedwith a relatively high :molecular weight branched-chain alcohol toobtain a high viscosity, the viscosity index has been .:relatively lowwhile the pour point has been found to be too high for practicalpurposes. On the other hand, when normal alcohols of relatively highmolecular weight have been used, al-- though the viscosity indices ofthe products have been found to be desirable, the pour pointshave beenfound to increase tremendously. Accord- ..ingly, it will be appreciatedthat there has been a demand for ester-type synthetic lubricantshavingugood .viscosities, relatively 1 high viscosity indices, andrelatively low pour points.

In accordance with the present invention, it

jhas now been discovered thatit is possible to produce anester-typesynthetic.lubricantposdetailed description.

Broadly stated, the present invention provides anew synthetic lubricanthaving a high viscosity index and a low pour point, which comprisesthereaction product obtained byreacting an. adipic acid monoester with anethylene glycol or thindiglycol in a'molar proportion of about =2:1,respectively.

Any ethylene glycol can be utilized as the glycol reactant. Ethyleneglyoclsare dihydricalcohols having the'general formula wherein n isan-integerequal to one or more, and preferably, between one and six.Non-limiting examples of the ethylene glycois which can be used'areethylene glycol, diethylene glycol, triethylene glycol, tetraethyleneglycolpand :hexaethylene glycol.

These glycols are readily available in commercial quantitiesand they arerelatively inexpensive.

The thiodiglycol reactant utilizable hereinihas the structure,HOCH2CH2S-CH2CH2OH. The manner ofpreparing this material is wellknown.The compound'is also available in commercial quantities. Thiodiglycol isclassified as a glycol ureactant'for thepurposes of the present inven-"tion.

The adipic acid monoestersuti-lizable in accordance with the presentinvention havethe structural formula:

HOOD

I H214. R000 wherein R is a branched-chain aliphatic group containingbetween about 6 and about 20 carbon atoms per radical, and,preferablybetween about 8 and about 16 carbon atoms. Examples of adipicacid monoester reactants are Z-ethylbutyl hydrogen adipate,.Z-ethyIheXyl hydrogen adipate, 1 methyl-4-ethyloctyl hydrogen adipate,2-methyloctyl adipate, 2-1nethylhepty1 adipate, and1-(3-ethylamy1)-4-ethyoctyl hydrogen adipate. These monoesters can bepre- 3 pared by any of several methods which have been proposed for thepreparation of monoesters [see C. Contzen-Crovert, Bull. Sec. Chem.Belg., 35, 165-98 (1926)]. gen adipate can be prepared as follows:

Example 1 The following reactants were placed in a 2- liter flaskprovided with a mechanical stirrer, a water trap, and a refluxcondenser:

366 g. (2.5 mols) adipic acid 500 milliliters xylene The mixture washeated to reflux and, after all of the adipic acid had dissolved, 129 g.(1.25 mols) of 2-ethy1butanol were added dropwise. Azeotropicdistillation of water was continued for 20 hours, at which time thereaction was complete. The solution was allowed to cool and theunreacted adipic acid was filtered off. Then the xylene solution waswashed with water to remove dissolved adipic acid, and it was dried. Thexylene was stripped at a pot temperature of 135 C. under a pressure of0.6 mm. The residual 2-ethy1butyl hydrogen adipate weighed 191 g. (83per cent yield, based on the acid consumed).

In order to produce the non-resinous products of this invention, theadipic acid monoester reactant and the glycol reactant are reacted in amolar proportion about 2:1, respectively. Particularly when operatingwith thiodiglycol, a slight weight excess of glycol reactant can beused. Such a weight excess should not exceed 30 per cent. In all cases,however, the excess glycol reactant is removed by distillation, or othersuitable means. To this extent, the molar proportion of reactants iscritical.

The reaction products contemplated herein may be prepared by any of theconventional Suitable solvents are the hydrocarbons of the benzeneseries boiling between 80 C. and 200 C., such as benzene, toluene,xylene, and cymene. Esteriflcation catalysts can be employed in thereaction of the present invention. Preferred catalysts are the strongacids, such as sulfuric acid, hydrochloric acid, and aromatic sulfonicacids. These catalysts can be used in amounts varying from about 0.1 percent to about 5 per cent by weight, based on the total weight of thereactants.

The time of reaction will depend on the reaction temperature and on thequantities of reactants involved. It is to be strictly understood thatthe method of esterification, and the time and temperature of thereaction are not critical factors in preparing the reaction products ofthe present invention.

The following specific examples are for the purpose of exemplifying thereaction products contemplated in the present invention. It is to beclearly understood that the invention is not to be considered as limitedto the specific glycol reactants and adipic acid monoester reactants, orto the operations and manipulations described in the examples. As willbe apparent to those Typically Z-ethylbutyl hydro- Esters prepared fromethylene glycols Example 2 The following reactants were placed in a 1- 7liter reaction flask, equipped with a mechanical stirrer, a thermometer,and a water trap provided with a water-cooled reflux condenser:

129 g. (0.5 mole) 2-ethy1hexyl hydrogen adipate 42 g. (0.275 mole)triethylene glycol 1.3 g. p-toluene sulfonic acid monohydrate 200milliliters xylene Stirring was commenced and the reaction mixture washeated until the azeotropic water-xylene mixture evolved and the xylenewas refluxing. The reaction was maintained under reflux at a temperatureof 143 C. for 24 hours, at the end of which period, the evolution ofwater from the esterification' ceased.

The reaction mixture was cooled and washed free of acid with a diluteaqueous solution of sodium carbonate, and then with water. The xylenesolution was dried with anhydrous sodium sulfate, following which, thexylene was removed by distillation at a pot temperature of 200 C. undera pressure of one millimeter. The grams of esterification reactionproduct (80.3 per cent yield, based on the adipic acid monoesterreactant) had the following properties:

Flash point F 435 Saponification number 357 Saponification number(theory) 352 Density 4 1.0103

Neutralization number 0.5

Example 3 Using the same apparatus as in Example 2, the followingreactants were charged:

129 g. (0.5 mole) 2-ethylhexyl hydrogen adipate '75 g. (0.25 mole)hexaethylene glycol 200 milliliters xylene The mixture was heated toreflux and the azeotropic removal of water was continued until itsevolution ceased. Then, 1.3 g. p-toluene sulfonic acid monohydrate wasadded and the reaction was continued under reflux for three hours. Theproduct, treated and isolated as described in Example 2, weighed 164grams (83.5 per cent yield, based on the adipic acid monoesterreactant). This reaction product had the following properties:

Flash point F 460 Saponification number 291 Saponification number(theory) 285 Density 4 1.0298 Neutralization number 1.0

Example 4 The following reactants were placed in a 1- liter flaskprovided with a mechanical stirrer, a water trap and a reflux condenser:

g. (0.652 mole) 2-ethylbuty1 hydrogen adipate 25 g. (0.391 mole)ethylene glycol 1.5 g. p-toluene sulfonic acid monohydrate 150milliliters xylene The reaction mixture was. heated for 20 hours underreflux conditions, at which time the azeotropic distillation of waterceased. The xylene Flash point F 385 Saponification number MSaponification number (theory) 462 Density 4 1.0216 Neutralizationnumber 0.1

Examples 5, 6, 7 and 8 The following reaction products were prepared :ina manner similar to that of the previous examples:

The utility ofthese products as synthetic lubricants is demonstrated bythe results obtained in the Lauson Engine Test. In accordance: with thistest, a single-cylinder Lauson liquid-cooled engine, with splashlubrication, .is operated at a speed of about 1825 R. P. M. The oil ismaintained at about 270 F. The engine is inspected at -hour intervalsand makeup oil is added at these times. After 100-hour operation of the.en gine, the oil is tested for acidity and viscosity, and the pistoncleanliness and the detergency of the engine are evaluated on thebasis'of 100. Also, the copper-lead bearings of the engine are weighedbefore and after the test, and the loss in weight in grams is reported.The product of Example .2, containing 0.75 per cent by weight of anoxidation inhibitor described in U. S. Patent No. 2,381,377, and aPennsylvania SAE #20 motor TABLE I Adipic Acid Monoester 2-ethyl-hexyln2-ethylbutyll-methyI-i-ethyloct l... l-(3-ethylamyl)-4-ethyloetyl.Glycol D1ethylene. Triethylene.-- Triethylene Diethylene. Flash Point495 F 420 F 415 465 F. Saponification Number 366 295 236. SaponificationNumber (Theory) .392 325 268. Density 4 1. 0428 0. 988.51 .1-l.. 0.9569.

It will be seen from the data presented in the foregoing examples, thatthe ethylene glycol reaction products of the present invention arepracoil, similarly inhibited (for purposes of comparison), weresubjected to the Lauson Engine Test. The results obtained are tabulatedin Table III.

tically neutral materials having a specific gravity of about one, orslightly greater. In all cases, the saponii'ication number agreesclosely with the theoretical value for a product which is completelyesterified. Further, these products have flash points that fall within arange which renders them comparable to light lubricating oils.

These products have high viscosity indices and very low pour points.Their excellence as synthetic lubricants is illustrated by the followingdata:

TABLE II E Kinematic Viscosity, cs. Example fisgzg P oint, at 100 F. at210 F.

It is apparent that the synthetic lubricant is appreciably superior tothe mineral lubricating oil in regard to cleanliness of the engine,minimum bearing corrosion, and low viscosity increase at the end of thetest period.

Esters prepared from thiodiglycol Example 9 The following reactants wereplaced in the reaction vessel described in Example 2:

208 g. (0.8 mole) 2-ethylhexyl hydrogen adipate 61 g. (0.4 mole+25%excess)thiodiglycol 2 g. p -toluene sulfonic acid monohydrate 2000milliliters xylene The reaction mixture was heated to reflux temperatureto remove the water of esterification. The reaction was continued for '7hours at 143- C., at the end of which time the evolution of water ofesterification had ceased.

The reaction mixture was cooled and washed free of acid with a diluteaqueous solution of sodium carbonate and then with water. The

xylene solution was dried with anhydrous sodium C. pot temperature under0.6 millimeter, the

.385 g. (1.0 mole) l-(3-ethylamyl)-4-ethylo6tyl hydrogen adipate 73 g.(0.5 mole+20% excess) thiodiglycol g. p-toluene sulfonic acidmonohydrate 300 milliliters xylene After washing, drying, and removingthe solvent, the reaction product was subjected to distillation at 200C. pot temperature, under 0.7 millimeter pressure, to remove excessthiodiglycol. Then, the product was stirred, at room temperature (about25 C.), with 10 grams of ignited aluminum oxide powder. Subsequently, anadditional l-gram portion of aluminum oxide powder was added, andstirring was continued for another hour. This treatment was .used toremove any residual acidity of the product. The material was filteredwith suction through filtering clay. The 369 grams of prodnot (86 percent yield, based on the adipic acid monoester reactant) had thefollowing propersulfate. Xylene was removed by distillation underatmospheric pressure. Finally, the residue was subjected to distillationat 200 C. pot temperature, under 0.4 millimeter pressure, to remove theexcess thiodiglycol. The 169 grams of product (69% yield based on theadipic acid monoester reactant) had the following properties:

Sulfur, percent 5.7 Sulfur, percent (theory) 5.3 Density 4 1.0095Saponification number 321 Saponification number (theory) 372 Example 1 0A large prepilot plant of the product of Example 9 was made in the themanner described therein. The gallons of finished product obtained hadthe following properties: 0

Sulfur, per cent 5.27 r Sulfur, per cent (theory) 5.31 Density 1-0036Sulfur, per cent 3.92 sapomficatlon number 336 Sulfur, per cent (theory)3.75

Saponification' number (theory) 372 251361131133, 2o 09597 This materialwas soluble in mineral lubricat- Saponification number 230 ing oils. Ithad a very good inhibitor response. Saponification number (theory) 262fligegxillllgxlggf :31: firovdlugfl raesggzrilclixelgrioafizgi gz Thethiodiglycol ester reaction products of the acid ester resin, known asAcryloid 710 was present invention havehlgh viscosity indices andblended therewith. This reaction product was low Pour m Thelr excellenceas -synthet1c unusually Stable toward hydrolysis and showed lubricantsis illustrated by the following data:

excellent dielectric properties. TABLE IV Example 11 Ki 1: v it Thefollowing reactants were reacted at c s. seas y viscosity Pour 158160 C.for 6 hours, as described in Ex- Emmpl" Index 8 ample 9: at 100 F at 210F. 24;e;g1.a(d0iair:ole) 1-methyl- -octylethyl hydrog2 gg 61 g. (0.4mole+25% excess) thiodiglycol 111 g g 5 g g; -es 2 g. p-toluene sulfonicacid monohydrate 200 milliliters xylene After Washin the ct, removin h UA great advantage of the thiodiglycol reaction vent, and remo ving ross:thiodig'lyco l at 580 Products of is that .they have good inherentanti-oxidation properties. In other words, they function satisfactorilyas lubricants without the necessity of blending antioxidants therewith.This quality is demonstrated by the 50 results of the Lauson EngineTest, wherein the product obtained weighed 239 grams, 87.5 per' centyield based on the adipic acid monoester reactant. It had the followingproperties:

Sulfur, per cent 4.87 product of Example 10 containing no oxidationSulfur, per cent (theory) 4.66 inhibitors was tested and compared withunin- Density 4 0.9851 hibited Pennsylvania SAE #20 motor oil. TheSaponification number 253 results obtained for each run are set forth inSapomfication number (theory) 366 50 Table V.

TABLE v Kinematic. Cleanliness g i i ng Hours N. N.

cs. Deter- Piston gency Top Bottom -i 10g 3.2g 76 68 0.004 0.000 SAE #2041s 11110 555 "ts "6E6 "0:55?

The products of the present invention are useful also as plasticizersand as intermediates in organic synthesis. The oil-solubility of thethi- 7'5- odiglycol reaction products suggests their use as Example 12The following reactants were reacted at HQ- C. for 3 hours, in themanner described in Example 9:

extenders for lubricating oils and as additives to impart valuableproperties thereto.

Although the present invention has been described with preferred.embodiments, it is to be understood that modifications and variationsmay be resorted to, Without departing from the spirit and scope of thisinvention, as those skilled in the art will readily understand. Suchvariations and modifications are considered to be within the purview andscope of the appended claims.

This application is a continuation-in-part of co-pending applicationSerial No. 6,019, filed February 3, 1948, now abandoned, by the sameinventor.

What is claimed is:

1. The non-resinous reaction product obtained by reacting an adipic acidmonoester having the formula, ROOC(CH2)4COOH, wherein R is abranched-chain aliphatic radical containing between about 6 and about 20carbon atoms, with a glycol reactant selected from the group consistingof an ethylene glycol having the formula, H(OCH2CH2)1LOH, wherein n isan integer varying between one and six, and thiodiglycol, in a molarproportion of about 2:1, respectively.

2. The non-resinous reaction product obtained by reacting an adipic acidmonoester having the formula, ROOC(CH2)4COOH, wherein R is abranched-chain aliphatic radical containing between about 8 and about 16carbon atoms, with a glycol reactant selected from the group consistingof an ethylene glycol having the formula, H(OCH2CH2)nOI-I, wherein n isan integer varying between one and six, and thiodiglycol, in a molarproportion of about 2:1, respectively.

3. The non-resinous reaction product obtained by reacting an adipic acidmonoester having the formula, ROOC(CH2)4COOH, wherein R is abranched-chain aliphatic radical containing about 8 and about 16 carbonatoms, with an ethylene glycol having the formula II (OCI-I2CH2) nOHwherein 11. is an integer varying between one and six, in a molarproportion of about 2:1, respectively.

4. The non-resinous reaction product obtained by reacting 2-ethylhexylhydrogen adipate with an ethylene glycol having the formula HOCI-IzCI-Iz) nOH wherein n is an integer varying between one and six, ina molar proportion of about 2:1, respectively.

5. The non-resinous reaction product obtained by reacting1-methyl-4-ethyloctyl hydrogen adi- 10 pate with an ethylene glycolhaving the formula, H(OCH2CH2)1L0H, wherein n is an integer varyingbetween one and six, in a molar proportion of about 2:1, respectively.

6. The non-resinous reaction product obtained by reacting an adipic acidmonoester having the formula, ROOC(CH2)4COOH, wherein R is abranched-chain aliphatic radical containing between about 8 and about 16carbon atoms, with thiodiglycol, in a molar proportion of about 2:1,respectively.

7. The non-resinous reaction product obtained by reacting Z-ethylhexylhydrogen adipate with thiodiglycol, in a molar proportion of about 2:1,respectively.

8. The non-resinous reaction product obtained by reacting an adipic acidmonoester having the formula, ROOC(CH2)4COOH, wherein R is abranched-chain aliphatic radical containing between about 8 and about 16carbon atoms, with triethylene glycol, in a molar proportion of about2:1, respectively.

9. The non-resinous reaction product obtained by reacting 2-ethylhexylhydrogen adipate with triethylene glycol, in a molar proportion of about2:1, respectively.

10. The non-resinous reaction product obtained by reactingl-methy1-4-ethy1octyl hydrogen adipate with triethylene glycol, in amolar proportion of about 2:1, respectively.

11. The non-resinous reaction product obtained by reacting an adipicacid monoester having the formula, ROOC(CH2)4COOH, wherein R is abranched-chain aliphatic radical containing between about 6 and about 20carbon atoms, with an ethylene glycol having the formula H OCHzCI-Iz)nOH References Cited in the file of this patent UNITED STATES PATENTSName Date Hentrich et al Aug. 22, 1944 De Groote et a1. Nov. 21, 1944Number

1. THE NON-RESINOUS REACTION PRONDUCT OBTAINED BY REACTING AN ADIPICACID MONOESTER HAVING THE FORMULA, ROOC(CH2)4COOH, WHEREIN R IS ABRANCHED-CHAIN ALIPHATIC RADICAL CONTAINING BETWEEN ABOUT 6 AND ABOUT 20CARBON ATOMS, WITH A GLYCOL REACTANT SELECTED FROM THE GROUP CONSISTINGOF AN ETHYLENE GLYCOL HAVING THE FORMULA, H(OCH2CH2) NOH, WHEREIN N ISAN INTEGER VARYING BETWEEN ONE AND SIX, AND THIODIGLYCOL, IN A MOLARPROPORTION OF ABOUT 2:1, RESPECTIVELY.